The present invention relates to a tissue stimulator system and methods of use.
The concept of using electronic stimulation systems for the purpose of controlling nerves or muscles is well known. These systems typically utilize an implantable or an external pulse generator. The external systems consist of a transmitter and antenna which transmits energy and/or stimulation signals transcutaneously through a patient""s skin to an implanted receiver. The receiver provides signal processing of the received pulses and transmits the energy derived therefrom to activate electrodes implanted adjacent to specific types of tissue to be stimulated. A system like the one described above has been disclosed previously in U.S. Pat. No. 3,727,616. It is also known in prior art where more than one pair of electrodes are activated such as U.S. Pat. No. 3,449,768.
Problems arise in these prior art systems where electrode placement fails to provide the desired physical response. It may also occur later if a change in patient condition or change in electrode position occurs. This failure may also be caused by improper polarity of the stimulated electrodes relative to one another. Furthermore, it is often required that the electrodes be implanted surgically adjacent to one or more nerve fibers. This type of procedure involves inherent risks due to the fact that it is often performed in close proximity to the brain or spinal cord or other sensitive nerves or tissues. It is therefore desirable to perform the electrode implantation only once to minimize the surgical risks to the patient as well as the financial burdens.
Moreover, even when a plurality of electrodes have been utilized, such that repeated surgical procedures are not required, the prior art systems did not provide for dynamic programming and reprogramming of different electrodes after surgery until U.S. Pat. No. 4,459,989 to Borkan. The Borkan patent ""989 disclosed an external stimulator system which allowed noninvasive programming of the stimulated electrodes. Each electrode was capable of assuming a positive, negative or open circuit status with respect to the other electrodes. This effectively allowed the electrodes to be xe2x80x9crepositionedxe2x80x9d non-invasively. That same programming ability (plus/minus/off) was later applied to totally implantable systems as well. The system had mono/biphasic control also.
Further improvements are described in U.S. Pat. No. 4,612,934 also to Borkan. The Borkan patent ""934 provides programming to the surgically implanted stimulator receiver to define electrode selection and polarity and stimulation pulse parameters. The pulse parameters included frequency, amplitude and pulse width. The impedance of the electrodes are measured and used to modify the programmed stimulation pulse as were inputs from measured physical parameters. A single stimulation pulse was developed and provided to any or all the selected electrode combinations. There was not the ability to provide individual pulses simultaneously to different selected electrodes. Also, the impedance of the individual electrodes were not measured, but only the electrodes as a group.
A tissue stimulation system includes an electrode assembly having at least three electrodes spaced to be stimulated in a patient. A programmable stimulator is connected to and provides stimulation pulses to the electrode assembly. A programming data in the stimulator defines, for each of the at least three electrodes, individual stimulation pulses of varying polarity and at least one of amplitude, frequency, pulse width and pulse shape.
The stimulator may include a pulse generator for each of the electrodes, or a common pulse generator for all the electrodes and a variable impedance circuitry for each of the electrodes. A variable impedance circuit may include a voltage divider or an analog switch, for example. The stimulator would individually control the amplitude and pulse width using the variable impedance circuit.
The stimulator can measure the impedance of each of the electrodes and modifies the stimulation pulse for each electrode defined by the programming data as a function of the measured impedance of that electrode.
Also, the stimulator may measure physical or physiological parameters and modifies the stimulation pulse for each electrode defined by the parameter data as a function of the measured parameters. The measured parameters may include one of the following: EMG, EKG, or EEG measurements. The measurement circuit may include chemical or biochemical sensors. The stimulator includes a signal input and modifies the stimulation pulses as a function of input signals on the signal input. The input signals may include processed audio or visual signals.
The stimulator may determine the position of the electrode from the measured parameters and modifies the stimulation pulses as a function of the determined position. A display is provided for showing the determined position.
An additional electrode spaced from the at least three electrodes is provided. The additional electrode has a surface area greater than the surface area of each of the at least three electrodes. The additional electrode is at least twice the surface area of each of the at least three electrodes. The additional electrode is spaced from the at least three electrode by at least 10 millimeters.
The programming data defines bipolar mode, monopolar mode and simultaneous bipolar/monopolar mode stimulation. The bipolar mode uses at least two of the at least three electrodes and the monopolar mode uses the additional electrode as an anode electrode and at least one of the at least three electrodes as a cathode electrode.
The present tissue stimulation system maybe used to perform a method of tissue stimulation by positioning the electrode assembly with the electrodes lying along a tissue to be stimulated in the patient and the stimulator connected to the electrodes. Stimulation pulses are provided from the stimulator to the at least three electrodes with independently assigned polarity and at least one of amplitude, frequency, pulse width and pulse shape. The stimulator may be external or preferably implanted.
The method may further include measuring the series impedance of each of the electrodes and modifying the stimulation pulse for each electrode defined as a function of the measured impedance of that electrode.
Additionally, physical or physiological parameters can be measured and the simulation pulse modified for each electrode defined as a function of the measured parameters. The measured parameters may include one of the following: EMG, EKG, or EEG measurements. Information may be obtained from at least one of pulmonary, cardiac or neuro monitors; and the stimulation pulses are modified as a function of the information and measured parameters.
Additionally, the relative position of the electrodes to the desired tissue to be stimulated may be determined using the measured parameters. The determined electrode""s relative position may be displayed. The display may show overlays of an image of the desired electrode position and/or movement on an x-ray or fluoroscopic image. The system provides feedback to a physician as the electrode is moved in real time.
The stimulation pulses may be modified as a function of the relative position. The measuring may include EMG measurements of specific muscles. The stimulation pulses are modified to determine the relative position of one or more of the individual electrodes.
The method may also include simultaneously providing stimulation pulses to at least two of the at least three electrodes in a bipolar mode and to an additional electrode as an anode and at least one of the at least three electrodes as a cathode in a monopolar mode.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.